Process for naphtha reforming



A. R.BERNAS ETAL 3,312,634

PROCESS FOR NAPHTHA REFORMING April 4, 1967 nal Filed Dec. 5. 62

ARNOLD RBERNAS JOHN S NEGRA INVENTORS BY.g -7 6ZQZQ AGENT United StatesPatent Office 3,312,634 Patented Apr. 4, 1967 9 Claims. (Cl. 252-373)This invention relates to the catalytic. steam reforming of normallyliquid hydrocarbons such as naphtha, to produce synthesis gasprincipally containing hydrogen and carbon monoxide, and is a divisionof application Ser. No. 242,564 filed Dec. 5, 1962, and now abandoned.An improved process has been developed for this purpose, in which thereaction is readily controlled to provide uniform temperature levelsthroughout the process stream, and conversion of the hydrocarbon isaccomplished without carbon deposition. The process of the presentinvention is a preferred procedure for accomplishing the naphtha reformprocess disclosed in US. patent application Ser. No. 160,- 749 filedDec. 20, 1961, now US. Patent No, 3,262,886.

The conversion of normally liquid hydrocarbons such as naphtha tosynthesis gas has been accomplished in several ways. One generalapproach is known as partial oxidation. In this procedure, liquidhydrocarbon is reacted with oxygen or oxygen-enriched air in anon-catalytic furnace at highly elevated temperature above 2000 F. Theliquid hydrocarbon is gasified and completely reacted at this elevatedtemperature, to yield a synthesis gas stream also containing freecarbon. This process is relatively costly since free oxygen must beprovided for the reaction. Another high-temperature procedure involvesthe use of refractory beds which are alternately heated and thenemployed as a heat source for hydrocarbon gasification in a cyclicprocess sequence. This type of procedure is subject to the drawbacks ofall cyclic processes, such as intermittent and alternating stream flow,lack of uniformity in stream composition, and excessive controlinstrumentation requirement.

In the present invention, a process is provided by means of whichnaphtha or similar normally liquid hydrocarbon may be catalyticallyreformed by reaction with steam, at temperatures in the range of 1600F., to provide synthesis gas. The improved process basically includes anew catalyst arrangement, in which a bed of metallic particlescomprising nickel is provided in combination with an adjacent bed ofconventional hydrocarbon reform catalyst such as nickel oxide depositedon kaolin or other carrier. Streams of vaporized naphtha, steam andprocess air are combined and the resulting process stream is passedthrough the .bed of metallic particles and then through the bed ofhydrocarbon reform catalyst. The beds are heated by conventional means.A fully reformed synthesis gas is produced.

The major novel aspect of the present invention involves the provisionof a bed of metallic nickel-containing particles prior to the bed ofconventional hydrocarbon reform catalyst. The bed of metallic particlesperforms several important functions. Due to high thermal conductivityof the particles, a substantially uniform temperature level prevails inthe process stream, Thus, localized overheating or temperature reductionwith consequent carbon deposition is prevented. When the reforming takesplace in a reformer tube mounted in a furnace, the high thermalconductivity of the metallic particles also serves to preventoverheating of the tube wall. In addition, because the metallicparticles contain nickel, a certain amount of endothermic steamreforming takes place. However, this reaction is relatively slow in themetallic bed, and thus the reaction is spread out and localized highreaction rate is avoided. A balance between heat transfer into theprocess stream and reform reaction rate is obtained, so that a uniformtemperature level is maintained. A high initial reform reaction rate isobjectionable, since this results in localized temperature reduction andconsequent carbon deposition.

In summary, the bed of metallic nickel particles has three majorfunctions. One function is to allow reforming to take place at 1600F.-1650 F. but at a slower rate than would occur with conventionalreforming catalyst. This reduces the amount of heat input through thetube walls which is required to maintain a minimum bed temperature of1600 F.1650 F., and thus lowers the tube wall temperature. A secondfunction is to permit reforming while avoiding carbon deposition, ascontrasted to other materials such as ceramic which promotes carbondeposition at 1600 F.-1650 F. A third function of the nickel particlesis to improve heat transfer from the tube wall to the process stream,because the effective thermal conductivity of the nickel bed is greaterthan that of a conventional reform catalyst bed.

It is an object of the present invention to catalytically reform naphthato produce synthesis gas.

Another object is to provide an improved process for catalytic reform ofnaphtha.

A further object is to provide a process for catalytic naphtha reformwithout carbon deposition.

An additional object is to provide a process for catalytic naphthareform with more uniform temperature distribution and improved controlof reaction rate.

These and other objects and advantages of the present invention willbecome evident from the description which follows. Referring to thefigure, a preferred embodiment of the present invention is shown, inwhich the two beds of reform material are disposed in a reformer tube 1which is provided with a central distributor tube 2. Tube 2 is coaxiallyaligned within tube 1, and extends down into bed 3 which consists ofmetallic nickel rings in this preferred embodiment. A lower bed 4consisting of conventional hydrocarbon reform catalyst, preferablyactivated nickel oxide deposited on kaolin, is also provided in thelower part of tube 1.

Tube 1 is typically mounted in a furnace, not shown, and is externallyheated by conventional burners, not shown. A stream of vaporized naphthais passed via 5 into central tube 2, and is mixed with a preheated mixedstream of steam and air which is passed via 7 into distributor tube 2.The resulting mixed process stream passes downward through tube 2, andis discharged through holes 6 into bed 3. Two principal reactions takeplace in tube 2 and bed 3. Part of the naphtha vapor is immediatelyoxidized by reaction with the air component of stream 7. This exothermicreaction does not result in a temperature rise, because endothermicreaction between steam and naphtha vapor also takes place in bed 3 andis catalyzed by the nickel rings. This reform reaction predominates,however concomitant temperature decrease in bed 3 is prevented due toheat transfer through tube wall 1 and into bed 3. The high heat transferrate which is obtained due to the presence of the nickel rings is highlyimportant in providing uniform temperature levels in bed 3, since carbondeposition is thus effectively prevented. Any sharp temperature risecould cause carbon deposition due to accelerated cracking of the naphthavapor, while a temperature decrease below 1600 F. at any point may alsocause carbon deposition due to unfavorable equilibrium in thesteam-carbon reaction.

The resulting partially reformed mixed process stream now passesdownward from bed 3, and contacts catalyst bed 4 Where complete steamreform of the naphtha and lower hydrocarbons derived from naphthacracking takes place. The resulting fully reformed synthesis gas streamis recovered via 8 from tube 1, and is passed to process utilization.

It will occur to those skilled 'in the art that the process of thepresent invention bears a superficial resemblance in terms of catalyticfunction to certain disclosures of the prior art. Thus, the concept ofproviding two beds or layers of catalytic material with differentactivity, and initially passing the process stream through the lessactive bed, is found in such prior art as US. Patents Nos. 2,801,159 and2,056,911 and Canadian Patent No. 597,393. However, it should alsobeevident that an im portant distinction in terms of function isachieved in the process of the present invention, due to the fact thatthe nickel rings have a high heat conductivity. Thus, the heatconductivity of prior art low activity catalyst beds is quite low, sincethese beds consist of refractorytype catalyst with deposited activatednickel or other catalytic component. Thermal conductivity of variouscatalytic carrier agents as contrasted to nickel is shown by thefollowing table.

It will be evident from the above table that representative refractorymaterials employed as catalytic carrier agents have thermalconductivities which are below 10% of that of nickel. Thus, a markedincrease in heat transfer rate and a substantially uniform temperaturelevel are obtained when nickel is employed in bed 3.

Numerous variations within the scope of the present invention will occurto those skilled in the art. Thus, it is possible and in some casespreferable to omit the central distributor tube 2. Thus, depending onthe type of liquid hydrocarbon involved, it may be preferable in somecases to merely spray or vaporize the liquid hydro carbon into the mixedair-steam input stream, and then to pass the resulting mixed processstream into bed 3.

Another variation or modification of the present invention involves bed3. The metallic particles of bed 3 are preferably nickel rings, howeverother particle shapes such as turnings, irregular pieces, mesh or ballsmay be employed in suitable cases. In addition, although the metallicparticles of bed 3 are preferably composed of substantially pure nickel,various metal alloys containing nickel such as 18-8 stainless steel mayalso be employed.

The hydrocarbon reform catalyst employed in bed 4 may be anyconventional catalytic agent. Typically, bed 4 will consist of nickeloxide deposited on or dispersed in support particles of a refractorycomposition or material such as those listed in Table 1 supra. Othercatalytic agents or elements such as zirconia, chromia, or molybdenumoxide may be employed, deposited on a suitable carrier. Additionalcatalytic agents and compounds are suggested in US. Patent No.2,056,911. It will be evident that a large number of suitable catalyticagents are available, for usage in bed 4.

Finally, the present invention is not restricted to an apparatusinvolving reformer tubes. Thus, the process of the present inventionalso broadly comprises a reform system consisting of a single largereform vessel or container, in which extensive beds of metallicparticles and hydrocarbon reform catalyst are provided. The beds may beexternally heated, or internal bayonet-type heaters may be dispersedthrough the beds. The beds may be vertically or horizontally adjacent toeach other, with corresponding vertical or horizontal flow of theprocess gas stream.

An example of an industrial application of the process of the presentinvention will now be described.

Example A typical petroleum naphtha was vaporized and reformed in a testrun of the process of the present invention. The naphtha specificationincluded the following:

ratio in the mixed process stream was 6 to 1, and air to carbon ratiowas 1 to 1. The catalyst consisted of nickel rings inlet half, andnickel oxide on kaolin plus binder in outlet half. The followingoperating conditions were maintained during the test run.

Residence time, sec 0.35 Linear velocity, ft./sec. 15 Space velocity,S.C.F. naphtha/hr.-ft. catalyst 655 Reform inlet temperature, 3F.1635-1655 Reform exit temperature, F. 1650-1675 Pressure, p.s.i.g150-160 These equilibrium operating conditions were maintained Withoutcarbon deposition in the apparatus employed in the process of thepresent invention. The vaporized naphtha was continuously reformed toyield a synthesis gas for ammonia manufacture.

We claim:

1. Process for catalytic steam reforming of a normally liquid naphthawhich comprises vaporizing said liquid naphtha, combining the vaporizednaphtha with steam and preheated air, contacting the resulting mixedprocess stream with a first catalyst bed consisting entirely of metallicnickel particles without a carrier at a temperature in the range of 1600F. to 1675 F., said first catalyst bed having high thermal conductivity,whereby partial steam reforming of the naphtha takes place withoutdeposition of free carbon, contacting the resulting partially reactedprocess stream at a temperature in the range of 1600 F. to 1675 F. witha sec- 011d catalyst bed comprising active hydrocarbon reformingcatalyst selected from the group consisting of nickel oxide, zirconia,chromia and molybdenum oxide deposited on a suitable carrier, andrecovering a final gas stream comprising synthesis gas substantiallyfree of unreacted naphtha and free carbon.

2. Process of claim 1, in which said active hydrocarbon reformingcatalyst comprises nickel oxide deposited on kaolin particles.

3. Process of claim 1, in which the initial mixed process stream isprovided with a molar steam to carbon ratio of about 6 to 1 and an airto carbon ratio of about 1 to 1, whereby said final gas stream comprisescrude ammonia synthesis gas.

4. Process of claim 1, in which said mixed process stream is contactedwith said catalyst beds at a pressure in the range of to p.s.i.g.

5. A process for the catalytic steam reforming of naphtha whichcomprises reacting a naphtha vapor stream with steam and preheated airin a non-catalytic reaction zone without reaching reaction equilibrium,contacting the resulting mixed process stream with a first catalyst bedconsisting entirely of metallic nickel particles Without a carrier at atemperature in the range of 1600 F. to 1675 B, said first catalyst bedhaving high thermal conductivity, whereby partial steam reforming of thenaphtha takes place Without deposition of free carbon, contacting theresulting partially reacted process stream at a temperature in the rangeof 1600 F. to 1675 F., with a second catalyst bed comprising activehydrocarbon reforming catalyst selected from the group consisting ofnickel oxide, zirconia, chromia and molybdenum oxide deposited on asuitable carrier, and recovering a final gas stream comprising synthesisgas substantially free of unreacted naphtha and free carbon.

6. The process of claim 5, in which said active hydrocarbon reformingcatalyst comprises nickel oxide deposited on kaolin particles.

7. The process of claim 5, in which the flow rate of said naphtha vaporstream relative to said steam and said preheated air provides an initialsteam to carbon ratio of about 6 to 1 and an initial air to carbon ratioof about 1 to 1 in said non-catalyst reaction zone, where- ReferencesCited by the Examiner UNITED STATES PATENTS 2,056,911 10/1936 Schilleret al. 23-2l2 2,940,840 6/ 1960 Shapleigh 482l5 2,943,062 6/1960 Mader252-373 FOREIGN PATENTS 597,393 5/1960 Canada.

20 LEON ZITVER, Primary Examiner.

H. T. MARS, Assistant Examiner.

1. PROCESS FOR CATALYTIC STEAM REFORMING OF A NORMALLY LIQUID NAPHTHAWHICH COMPRISES VAPORIZING SAID LIQUID NAPHTHA, COMBINING THE VAPORIZEDNAPHTHA WITH STEAM AND PREHEATED AIR, CONTACTING THE RESULTING MIXEDPROCESS STREAM WITH A FIRST CATALYST BED CONSISTING ENTIRELY OF METALLICNICKEL PARTICLES WITHOUT A CARRIER AT A TEMPERATURE IN THE RANGE OF1600*F. TO 1675*F., SAID FIRST CATALYST BED HAVING HIGH THERMALCONDUCTIVITY, WHEREBY PARTIAL STEAM REFORMING OF THE NAPHTHA TAKES PLACEWITHOUT DEPOSITION OF FREE CARBON, CONTACTING THE RESULTING PARTIALLYREACTED LPROCESS STREAM AT A TEMPERATURE IN THE RANGE OF 1600*F. TO1675*F. WITH A SECOND CATALYST BED COMPRISING ACTIVE HYDROCARBONREFORMING CATALYST SELECTED FROM THE GROUP CONSISTING OF NICKEL OXIDE,ZIRCONIA, CHROMIA AND MOLYBDENUM OXIDE DEPOSITED ON A SUITABLE CARRIER,AND RECOVERING A FINAL GAS STREAM COMPRISING SYNTHESIS GAS SUBSTANTIALLYFREE OF UNREACTED NAPHTHA AND FREE CARBON.